Beam sensors are usually used in order to perform various types of control for improving the running safety of vehicles. Such a beam sensor transmits probing beams, such as laser beams, ultrasonic waves, or millimeter waves, and receives reflection beams, thus detecting targets located around a vehicle.
Such a beam sensor is mounted to a predetermined mount position of a vehicle while the beam axis is aligned with a previously designed axis position such that each probing beam is irradiated within a predetermined irradiation range. For this reason, if any factor causes the mounted position of the beam sensor to be deviated from the predetermined mount position, the beam axis may be deviated from the previously designed axis position. This may result in radar waves being out of the predetermined irradiation range. This may deteriorate the detection accuracy of targets to be detected by the beam sensor, deteriorating the accuracy of the various types of control for improving the running safety of the vehicle.
In view of these circumstances, technologies are proposed for detecting axial misalignment of beam sensors.
For example, a technology disclosed in patent document 1 detects a stationary object, which is located at one side of the travelling direction of a vehicle and extends in the travelling direction, and detects, based on captured images, that there are no other objects adjacent to the stationary object. Then, the technology transmits a radar signal at the detecting operation, and determines whether the difference between the distribution direction of each reflection point of the radar signal by the stationary object and a reference direction is equal to or more than a threshold value. The technology determines, based on the results of the determination, whether there is axial misalignment of the radar beam axis in a horizontal plane including the radar beam axis, i.e. the plane extending along the vehicle width direction and including the radar beam axis.
Additionally, a technology disclosed in patent document 2 detects a vanishing point in accordance with an image captured while a vehicle to which a laser beam sensor is installed is running.
Then, during adjustment of the laser beam axis, i.e. while the vehicle is stopped, the technology detects, based on the detected vanishing point and the transmitting direction of a laser beam, the difference between the transmitting direction of the laser beam and the forward direction of the vehicle, and corrects the transmitting direction of the laser beam accordingly.